A three-dimensional (3D) look-up table (LUT) may be generated from a color grading process by a colorist or it may be estimated by an encoder (for example, using an original signal in one color space and the corresponding signal in another color space). The 3D LUT may need to be sent in a bitstream from the encoder to a decoder, such that the decoder may apply a color gamut conversion process (e.g., the same color gamut conversion process) during inter-layer processing.
Signaling overhead of 3D LUT may be significant, because the dimension of the table may be large. For example, a sample bit-depth may be 8 bits and a unit octant size may be 16×16×16 (e.g., the color space may be partitioned to a representation of 16×16×16 octants) and, as such, there may be 17×17×17 entries in the 3D LUT table. Each entry of the 3D LUT may have 3 components. Thus, the total uncompressed table size may be 117,912 (17×17×17×3×8) bits, which may result in significant signaling overhead. With this amount of overhead, 3D LUT may have to be signaled at a sequence level, because, for example, individual pictures may not be able to afford such an overhead. At the sequence level, each of the pictures in a sequence may use the same 3D LUT, which may result in a sub-optimal color gamut conversion and/or may degrade enhancement layer coding efficiency. The colorist may (for artistic production reasons) change the color gamut from picture to picture or from scene to scene, and so picture-level signaling of the 3D LUT may be required for effective color gamut prediction.